EV Charging Part 1: The Technical Demands of EV Charging

Probably the most important infrastructure subsystem for the success of electric vehicles (EVs) is the national electric grid – powerplants, transmission lines, substations, etc. The “last mile” of this system, where the electric grid connects to the EVs themselves, is the EV charging station.

EV Charging Basics

Today there are three types of charging stations used with EVs:

• Level 1 EV Chargers: Almost exclusively for home EV charging, these chargers take AC voltage from a standard 110VAC home outlet, and provide that AC voltage to the EV. The charger communicates with the AC-DC inverter in the EV and with the EV’s battery management system to “meter” the current going into the EV; this is to avoid overheating the batteries, and to shut down the charger when the EV’s batteries are fully charged and/or when the EV is disconnected from the charger. The maximum power output of a Level 1 charger is 1.44 kW (12 amps at 120VAC). Level 1 chargers tend to be fairly low cost ($100-$200), and are generally not repairable.

• Level 2 EV Chargers: In a general sense, level 2 chargers work exactly like Level 1 chargers, but they run off of 240VAC power instead of 120VAC power. Level 2 chargers can supply up to 19.2 kW of power (80A at 240VAC, depending on the EV’s maximum power input), allowing them to charge the EV’s batteries over 13x faster than a Level 1 charger. Many home EV chargers are built to support both Level 1 and Level 2
  charging and are known as Level 1/2 chargers.

  Most commercial chargers (those used in public places and in parking areas of multi-tenant residential buildings) today are Level 2 chargers. Level 2 chargers in public places are typically operated by charging network companies, while ones in multi-tenant buildings may be operated by charging network companies or provided by the building owner. The primary difference between these Level 2 chargers and “home use” Level 2 chargers is that they include an “access system” which ensures that the charger can only be used by either a resident of the multi-tenant residential building, or by a customer with an account with the charging network (though some include credit card readers to allow anyone to use them). A Level 2 commercial charger from ChargePoint is shown to the right.
  

• DC Fast Charger (or “Level 3 Charger”): Level 2 chargers are limited in their ability to charge an EV quickly due to limitations in the built-in inverter of the EV, as well as the power output capability of the charging station. DC fast chargers (also known as ‘Level 3 chargers’) get around these limitations by providing DC power directly to the EV battery system. Some of these chargers can provide 250 kW of power (or more) to an EV. A 250 kW DC fast charger can fully charge an EV with a 100kW battery pack in roughly 24 minutes, compared with a Type 2 charger that would take over 5 hours, assuming the batteries were fully discharged in both cases.

  For most of these chargers, the power conversion unit, the box that takes AC power in and converts it to DC power, is separate from the “dispenser,” the box that holds the cable and dispenser nozzle and provides the access system interface for the user. The power conversion units tend to be large (think the size of a commercial refrigerator) and somewhat noisy due to their cooling fans. Because of this, they tend to be located in a separate area from the dispenser and connected by an underground DC power cable and a data cable to the dispenser.

The connection to the EV for Level 1 and Level 2 chargers is through a “dispenser nozzle” that, from the outside, looks like a gas pump nozzle; this dispenser nozzle is standardized under the Society of Automotive Engineers (SAE) Standard J1772 (see belo left picture). Level 3 chargers build on this by adding two high-amperage DC plugs, and are known as Combined Charging System (CCS) dispenser nozzles, as shown in the second picture below. Some DC fast chargers (Tesla Superchargers in particular) utilize proprietary charger nozzles, primarily for the purpose of providing more current than CCS charger nozzles are capable of providing. The cables connecting these dispenser nozzles to their dispenser tend to be liquid-cooled. Many companies make adapters to allow Tesla SuperChargers to be utilized with EVs having a CCS connector.

What is Driving DC Fast Chargers in the EV Charging Space?

Until the advent of DC fast chargers, “range anxiety” (worrying whether you could reach your destination before your EV would need charging) was a big issue for EV owners, especially those going on long-distance or cross-country trips. Range anxiety in the days before DC fast chargers was made worse by the long time it would take to charge the vehicle using a Level 2 charger; oftentimes charging would have to happen overnight. It was also made worse by the poor reliability of commercial Level 2 chargers; recent surveys have put the percentage of non-operable deployed Level 2 chargers in public areas at roughly 50%.

DC fast chargers are, to a large extent, mitigating range anxiety concerns. This is especially true of Tesla, where the fast charging capabilities of Tesla SuperChargers has been a big factor in driving the sale of Tesla EVs. As such, most of the new chargers being publicly deployed today are DC fast chargers; there are an estimated 43,152 of these currently deployed across 10,662 locations. Moreover, DC fast chargers tend to be significantly more reliable than Level 2 chargers since they were designed from the start for commercial usage and conditions, and most Level 2 commercial chargers are adaptations of consumer Level 2 chargers with the addition of a credit card reader.

As can be expected, DC fast chargers are significantly more expensive to build and deploy than Level 2 commercial chargers. There are several reasons for this:

• Higher electronics cost: Level 2 commercial chargers are relatively simple; in most cases they essentially are a mash-up of a home Level 2 charger and a credit card reader. DC fast chargers, however, have hundreds of pounds of electronics in them, from high-voltage transformers to AC-DC inverters to liquid cooling systems to fault reporting systems. Plus, they have a credit card reader…

• Significantly higher power requirements: Whereas even a Level 2 charger can run from a home electricity feed, a single DC fast charger can use enough electricity to power a good-sized subdivision. That means a DC fast charger “farm” with tens of chargers probably requires its own electricity substation, even if it has solar panels and battery storage. This has a huge impact on both the cost and time it takes to field public DC fast chargers.

• Periodic maintenance requirements: Most DC fast chargers have requirements for periodic maintenance, often to clean out cabinets, fans, and filters. In contrast, the typical failure mechanism is breaking the cable connecting the charger to the dispenser nozzle. The positive side-effect of this maintenance is that charging station failures are likely caught much earlier; in contrast, commercial Level 2 charger stations are often “unmanned,” with failures more likely reported by consumers than found ahead of time.

While these factors would seem to make DC fast chargers harder to deploy (and they indeed do), the consumer demand for DC fast chargers far outweighs these issues. This is one of the reasons why Tesla SuperChargers now support CCS-capable DC fast charging for non-Tesla EVs – DC fast chargers made Tesla about $1.7B in revenue in 2023, and is expected to produce $7.4B in revenue in 2030. This is nearly four times the revenue that ChargePoint made in 2023, not to mention how much in additional EV sales the SuperCharger network enabled. Seems like a good reason to deploy EV chargers. In our next blog in this series, we will explore what charger manufacturers and their infrastructure ecosystem partners are doing to reduce costs and improve the efficiency of DC fast chargers.